Let’s look at bones:
You know how all the commercials say that the calcium in milk helps build strong bones? Well, resistance training is another essential component.
What exactly is resistance training?
Defined by ominous Google, resistance training is any exercise in which muscles contract against external load. This load can be body weight, band resistance (with mini loops or resistance bands), or fixed weight (utilizing barbells, dumbbells, kettlebells, machines, and weight plates).
There are two important things to know about the body:
- Bone is constantly being remodeled (formed) and resorbed (degraded). In adults, about 10% of bone is remodeled every year.
- The body likes to be as efficient as possible with muscle and bone. In order to avoid spending extra energy lifting heavier than necessary bone or muscle day to day, the body will decrease bone density or muscle mass if they are not regularly used.
How does resistance training stimulate bone growth?
The bones in our bodies have a threshold called minimal essential strain (MES). This is the amount of weight [load] a bone must experience for new bone growth to be stimulated and it is regulated by bone cells so that forces experienced on a regular basis don’t exceed it. The process of bone adaptation begins within the first few weeks after a stimulus above MES, but it is also a long term process; it requires six or more months and regular forces greater than MES to result in increased bone density. Activities that generate forces greater than MES include those that are weight bearing and high intensity (i.e. resistance training).
Why is stimulating bone growth important?
- Adequate bone strength and thickness are important for preventing injuries such as fractures and stress fractures.
- It is important to stimulate bone growth because through the majority of our adult lives our bone density is actually decreasing, especially in women. Our bone density peaks when we are between 25 and 40 years old and decreases from that point on. It is important that we get our peak as high as possible through our 20’s and 30’s, and it is essential for those over 40 to preserve as much bone density as they can. Regular resistance training by older adults has been shown to offset age-related declines in bone health.
- In those with osteoporosis or osteopenia (diseases where bone mineral density is reduced to critically low levels), resistance training can beneficially stimulate bone growth .
Here’s two images depicting the prevalence of fractures from weak, osteoporotic bones that occur with age and gender.
How should one exercise to achieve increases in bone density?
There are a couple components to consider in order to best stimulate bone growth with your workouts:
- Specificity of Loading: Exercises must directly load a particular region of the skeleton to induce bone growth. For example, bodyweight squatting loads the pelvis and leg bones but not the arm bones or ribcage. Pushups load the arm bones but not the leg bones.
- Speed, Direction, and Variability of Loading: Loading of bone is only osteogenic (bone-growth inducing) if the weight is moved (it can’t just be held in place (static). Also, variety in exercises (changing exercises every 3-4 weeks) ensures that all bones receive stimulus.
- Proper Exercise Selection: Best exercises for inducing bone growth involve heavy loads, multiple joints, and forces directed through the spine and hips. Examples of these type of exercises are squat, lunge, deadlift, row, and press variations.
- Progressive Overload: Once a bone adapts to a given strain level, the MES (stimulus for bone to form) is higher. Overtime, the weights lifted or intensity of exercise must gradually increase in order to continue stimulating bone growth.
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Bilezikian, J.P., Raisz, L.G., Rodan, G.A.. Principles of Bone Biology, Second Edition. Volume 1. Academic Press, 2002.
McNeely, E.. Training to Improve Bone Density in Adults: A Review and Recommendations. U.S Sports Academy. July 9, 2010.
Moreira, Linda Denise Fernandes, Oliveira, Mônica Longo de, Lirani-Galvão, Ana Paula, Marin-Mio, Rosângela Villa, Santos, Rodrigo Nolasco dos, & Lazaretti-Castro, Marise. (2014). Physical exercise and osteoporosis: effects of different types of exercises on bone and physical function of postmenopausal women. Arquivos Brasileiros de Endocrinologia & Metabologia, 58(5), 514-522. https://dx.doi.org/10.1590/0004-2730000003374